
The Thursday night success was sealed with a match tiebreak, 6-1, 3-6, 10-4 over Gisela Dulko and Juan Chela.
Jankovic began her day of playing in pain by quitting with a right hamstring strain picked up a day earlier, handing Dulko a 6-7 (10-12), 2-0 win.
Djokovic, third in the world like his Serb teammate, came good for his Balkan nation as he prevailed over Chela 6-2, 6-3 in men's singles for 1-all in the tie.
That set the stage for the showdown which by rights should not have happened as the brave Jankovic threw her Australian Open hopes to the winds by playing in the deciding mixed doubles rubber which sealed a Friday night final against the four-time champion US.
The Serbs won it 6-1, 3-6, 10-4 (match tiebreak) for a 2-1 final result in the tie.
Serena Williams and Mardy Fish were untroubled earlier in a 3-0 troll past the Australia of Alicia Molik and Peter Luczak.
Jankovic was close to tears of joy when the win was sealed. The 22-year-old said she would give her all for Serbia, in the final despite her hobbling.
"I have no idea why I'm playing. I have a Superman partner, he's just unbelievable, if he was not here we would not have won. Thanks to him we're in the final."
The Serb added: "My injury was worse today, it's quite inflammed, but I tried my best in singles. My leg just couldn't hold up.
"I'm having a hard time on the court. I'll try my best, I'm risking injury and my career, but it's such a pleasure to play here. I still have a lot of motivation to make one or two shots in the match. I'm playing with the pain and I still try to win. I want Serbia to be the best," Jankovic said.
The hardy pair will be playing a third tie in as many days.
"The most important thing is that we won," said Djokovic. "We were both tired and she was injured even more. We're struggling but thanks to the crowd support we came through."
American Fish fired 25 acres to consolidate the fifth trip to the final for the US with a defeat of Australian Peter Luczak 7-6 (7-5), 7-6 (12-10).
The American needed six match points to finally prevail after saving Luczak's three chances to take the tight match into a third and deciding set.
Williams had already guaranteed her side a place the title shoootout by beating Australian Molik 6-2, 7-6 (9-7) to ice the finals spot.
The US won its last title at the tournament through Williams and James Blake in 2003.